1. Field of the Invention
The present invention relates to vehicle motion estimating systems for estimating one or more vehicle motion variables by using a predetermined vehicle model.
2. Description of Prior Art
Recent advances in automotive electronics have been increasing the demand for various sensors for sensing a wide variety of vehicle motion variables. However, only a few of the motion variables are easy to sense, and only a few sensors such as a yaw rate sensor and a lateral acceleration sensor are known. Moreover, it would be undesirable and difficult to mount as many sensors as the required vehicle motion variables are of many kinds.
3. Description of Other Information
The above-mentioned U.S. patent application Ser. No. 837,170 proposes a vehicle motion estimating system which is designed to determine one or more vehicle motion variables by solving a mathematical vehicle model consisting of equations of vehicle motion. This system can determine various vehicle motion variables without using any sensor for sensing such motion variables. With this estimating system, it is not necessary to provide a sensor for each vehicle motion variable, and it is possible to determine the vehicle motion variables which are difficult or impossible to sense.
In order to improve the accuracy of calculation in determining various vehicle motion variables by using such a mathematical model; (1) The accuracy in mathematical modeling must be sufficiently high. That is, the model must be one having many degrees of freedom. (2) Especially when integration is performed digitally, it is desirable to make an interval of integration short, and to reduce an error of integration.
However, microcomputers for on-board automotive applications do not have a sufficient computing ability to fulfill the above-mentioned requirements. If a usual on-board automotive microcomputer is arranged to satisfy the above-mentioned requirements, then the operation time will become too long to perform a real-time vehicle motion estimation.
On the other hand, analog computers are advantageous in computing speed. However, it is difficult to ensure satisfactory dynamic range and noise margins in an analog computer.